XML Schema Chao-Hsien Chu, Ph.D. School of Information Sciences and Technology The Pennsylvania State University ElementType AttributeType XML Declar. Schema Declar.

Purposes of DTD  What elements should be presented?  How many of each element were required?  What kind of element content was permitted?  In what order the elements should appear? DTD is the modeling language for XML, which define the structure of a XML document. An DTD file provides the following information:

Components of XML Systems XML Parser (Processor) XML Application XML Document (Contents) XML DTD (Rule) Well-Formed (Syntax) Validate (Structure)

What is XML Schema  DTD is the original modeling language for XML. It has the following deficiencies: - DTD did not follow the regular XML syntax, thus it requires a special parser to validate. - DTD did not support much of data types. - DTD is weak in extensibility.  Schema is the new modeling language for XML,which closely follows XML syntax.

Problems with DTD If the DTD statement for element Quantity is: Then which of the followings syntaxes are valid? 5 _________ hello _________ 5.5 _________

Facts About XML Schema  Schema documents use XML syntax and are therefore XML documents.  Schemas are XML documents that conform to DTDs, which define the structure of a XML document.  Many organizations and individuals are creating DTDs and schemas for a broad range of categories (e.g., financial transactions, medical prescriptions, etc.). These collections called repositories which are often available free for download from the web.

Why Schema is Better?  XML Schema has Support for Data Types  XML Schemas use XML Syntax  XML Schemas Secure Data Communication  XML Schemas are Extensible  Well-Formed is not Enough

XML Example (1) <shiporder orderid="889923" xmlns:xsi=" xsi:noNamespaceSchemaLocation="shiporder.xsd"> John Smith Ola Nordmann Langgt Stavanger Norway

XML Example (2) Empire Burlesque Special Edition Hide your heart

Components of Schema  XML Declaration  Comments  Schema Declaration  ElementType Declarations  AttributeType Declarations

Example of DTD File (1) Attribute List Declarations Element Type Declarations

Example of DTD File (1) Element Type Declarations

XML Schema (1)

XML Schema (2)

XML Declaration  Is used to provide information regarding processing such as processor (name and version), of the processor Syntax:  Examples: 

Comments  A place to write a note for reminding, simple documentation, or commenting out codes for debugging, etc., which will not be seen by the end users. <!-- This is a comment area -->  You can use any character inside the comment area except “--” itself  There is no limitation on the length of the comment area.

Selected XML Schema Data Types  boolean. 0 (false) or 1 (true).  char. A single character.  string. A series of characters.  float. A real number.  int. A whole number.  date. A date formatted as YYYY-MM-DD.  time. A time formatted as HH-MM-SS.  id. Text that uniquely identifies an element or attribute.  idref. A reference to an id.  enumeration. A series of values from which only one may be chosen.

Date and Time Data Types NameDescription  DateDefines a date value  dateTimeDefines a date and time value  DurationDefines a time interval  gDayDefines a part of a date - the day (DD)  gMonthDefines a part of a date - the month (MM)  gMonthDayDefines a part of a date - the month and day (MM-DD)  gYearDefines a part of a date - the year (CCYY)  gYearMonthDefines a part of a date - the year and month (CCYY-MM)  TimeDefines a time value

Numeric Data Types Name Description ByteA signed 8-bit integer DecimalA decimal value IntA signed 32-bit integer IntegerAn integer value LongA signed 64-bit integer negativeIntegerAn integer containing only negative values (.., -2, -1.) nonNegativeIntegerAn integer containing only non-negative values (0, 1, 2,..) nonPositiveIntegerAn integer containing only non-positive values (.., -2, -1, 0) positiveIntegerAn integer containing only positive values (1, 2,..) ShortA signed 16-bit integer unsignedLongAn unsigned 64-bit integer unsignedIntAn unsigned 32-bit integer unsignedShortAn unsigned 16-bit integer unsignedByteAn unsigned 8-bit integer

Advantages of XML Schema  Consistency. It follows XML syntax.  Extensibility. It includes data type and namespaces.  Exchangeability/manipulability.  Rigid specification.  Ease of use. Can use with XML API such as DOM and SAX.

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